Generally, magnetic recording media in the shape of a tape are widely used (often herein simply a "magnetic tape"). Such a tape shaped magnetic recording medium is prepared by coating a magnetic coating composition containing ferromagnetic particles on a surface of a non-magnetic support such as a polyester film, providing magnetic orientation thereto, drying, calendering and cutting to the desired width.
If a cut surface of a tape breaks off, cracks or has powders attached thereto (dust from cutting the tape, hereafter merely referred to as "dust"), powder-off and edge damage are likely to occur, causing dropouts and, as a result, greatly decreasing the commercial acceptability of the magnetic recording medium. Accordingly, upon preparing a magnetic recording medium, it is very important to finish the cut surface of a tape very neatly.
A shear cutting method using an edged tool of e.g., super-hard alloy including tungsten carbide (hereinafter often referred to as "a knife") as described in Japanese Patent Publication Nos. 4635/86 and 39275/84 and Japanese Patent Application (OPI) No. 202385/87 is generally employed for cutting a magnetic recording medium, and a knife elaborate enough to cut the medium into 1/2 inch width only with variation of .+-.10 .mu.m or smaller is used. (The term "OPI" as used herein means an "unexamined published Japanese patent application") Various improvements have been proposed for such cutting devices. However, recently, a highly smooth cut surface is required for magnetic recording media with a tape shape, but improvements as to cutting methods and devices have not yet satisfactorily responded to the requirements of the art.
With a conventional cutting process, it is unavoidable that the edge of a knife wears out and it is necessary to regularly grind the edge of the knife or change the knife. Therefore, knife wear should be reduced as much as possible to increase the production efficiency of magnetic recording media with a tape shape.